class Dog():
    """ 一次模拟小狗的简单尝试 """

    def __init__(self, name, age):
        self.name = name
        self.age = age

    def sit(self):
        """ 模拟小狗被命令时蹲下 """
        print(self.name.title() + " is now sitting.")

    def roll_over(self):
        """ 模拟小狗被命令时打滚 """
        print(self.name.title() + " rolled over!")


my_dog = Dog('ddd', 3)
my_dog.roll_over()
my_dog.sit()
